Why aren't we comfortable at 98.6deg F, zero humidity?

Apologies if this has been asked/answered many times before.

Are any warm blooded animals most comfortable at temps around their body heat?

Is it that humans put out body heat–say, 20 deg. (I’m free-flying here), which is why 78 deg. or so is our sweet spot?

Yes. The engine that powers us is not 100% efficient (obviously) and gives off considerable waste heat. We are most comfortable in a temperature cooler than body heat because it makes it easier to get rid of that waste.

I’m pretty comfortable at 98 degrees with very low humidity, as long as I’m not exposed to the sun and I have plenty to drink. I’ve only been lucky enough to experience that a few times (in California and Arizona).

The body produces heat. In order for the body to stay at a steady temperature, that heat must be lost to the environment. And in order for heat to be lost the environment, there has to be a gradient of something closely related to temperature between the body and the environment. It’s not quite temperature itself that’s relevant to this: We can fudge it a bit by sweating. But that only goes so far.

Unca Cecil’s column

Both **Cecil **and **Chronos **mention waste heat, but doesn’t the body want to maintain that temperature for various biological processes to operate effectively? That is, we want to lose heat, but only so much.

Ideally, we want to lose heat at roughly the same rate that we make it.

Which is why the human body has a complicated system for core temperature regulation. Humans can tolerate a significant range of temperature variation in air, but for ambient temperatures in excess of about 90 °F it is necessary to reject excess heat via evaporative cooling (sweating), and at about 130 °F the human body can no longer effectively thermoregulate and will experience hyperthermia.


And on the opposite extreme, you have vasoconstriction, shivering, limb adduction, and hunger. I find vasoconstriction to be the coolest (heh) because it not only reduces blood flow, but it also causes heat exchange between vein and artery to occur higher up the limb. That’s why your fingers get cold before your arms. Shivering is pretty cool, too, because it seems like it just makes you move muscles to generate heat. But it’s really the only way to do that while holding still. See, your brain could just tell you to run around in circles, but that would cause the apparent wind to cool you down by convection, so instead, we’ve evolved to “microexercise” in place.

Over the evolutionary timescale, animals gets shorter limbs and counter-current blood flow as well as extra hair and distributed fat to insulate, as opposed to concentrated in one body part (compare a whale’s fat location to a camel’s).

Interestingly, many a stranded hiker has eaten snow, thinking it’s important to hydrate, and realizing too late that putting that much cold stuff right in the core of the body is a bad idea. If you’re ever stuck like that, hold snow in your hands to melt it before drinking.

Yes. That’s why we’re uncomfortable in a 100 degree desert, but also in a frozen tundra. Our bodies are very picky.

This may seem a silly question but…does someone who can tolerate a higher temperature (in fact, prefers it) of say 82 degrees over the normal 74 degrees mean that they produce less waste heat? Therefore they are comfortable with a higher temp because they are putting off less heat? Or does it have to do with something else entirely?

I don’t think there’s any doubt about that. Hot climates have tiny animals like lizards and ants. Cold climates have big animals like moose, bears, and whales. The reason is because surface area increases slower than volume as you scale up. So there’s more mass trying to vent heat through the same amount of surface area. Thus, the bigger you are, the harder it is to pass your heat off to the environment. Big people tend to make more heat and retain more heat than little people. So the people that are comfortable in hot temperatures tend to be women and small men.

Doesn’t humidity make a huge difference in what temperatures you can tolerate? In a low humidity enviroment like a sauna it’s perfectly possible to tolerate and even enjoy temperatures up to 230 °F or more.

A constant temp of 98.6 is what we all get the first 9 month. Is it comfortable? Humidity doesn’t really factor into a liquid environment though.

Maybe I am way off base but this statement by Cecil is missing the humidity/perspiration/evaporation angle.

If i am sitting in the shade in 98 Deg (F) and the relative humidity is very low, as long as I am hydrated and in good health I should have no problem and the shade will make me happy.
Back 40 years ago during training maneuvers on the Fort Riley base a shade tree was golden!
I live in a humid area and am very uncomfortable in the heat. When I was in the desert and had to preform in rescue drills I was able to because of the low humidity.
My cooling system that our creator designed works perfectly in low humidity.

Lots of elephants in the Congo.

And African elephants have huge ears, to increase their surface area per volume.

True, but they are somewhat larger than “lizards and ants”.

“Scaling, scaling, over the open sea…”

This is a good question. I’m comfortable at temperatures that make other people whine about heat (I whine about the cold instead) and my average temperature is barely above 98, and it frequently dips below that as well. This is of course anecdotal evidence, but I wouldn’t be surprised if other heat-tolerant people were similar.